With recent advances in intravenous (IV) infusion pump technology, increased emphasis has been placed on establishing treatment protocols which provide a patient with earlier opportunities for greater freedom of movement. To this end, there has been a great deal of interest in the development of light weight and easy-to-use portable pumps which can be used to augment or supplement the infusion protocols which are now being accomplished using the more precise but less mobile fixed station infusion pumps. Examples of infusion pumps which are very precise and effective for their intended purposes, but which are not primarily intended for ambulatory use by a patient, include the volumetric IV pump disclosed in U.S. Pat. No. 3,985,133 which issued to Jenkins, and the peristaltic IV infusion pump disclosed in U.S. Pat. No. 4,617,014 which issued to Cannon et al., both of which are assigned to the assignee of the present invention.
For maximum flexibility in the implementation of an extended and comprehensive infusion therapy program there is a recognized need for a portable IV infusion pump or device which can be effectively used by a patient regardless whether the patient is admitted to the hospital or is in an outpatient status. Preferably, the pump can be initially set up and operated by an ambulatory patient, with little or no assistance from trained medical personnel. As a consequence, because the portable pump is most likely to be operated and used by a patient without the assistance or supervision of a medically trained attendant, the pump needs to be both reliable and accurate. This is particularly so when sophisticated medicament infusion regimens are prescribed.
To achieve the advantages of a portable ambulatory pump, several types of mechanisms have been suggested. Typically, these mechanisms are mechanical, rather than electrical. At least to some extent, this is so because electrically operated pumps require a power source and, thus, they must either include a battery or be connected to an external power source. If they require a battery, they are typically heavy or have a limited useful operating life. On the other hand, if they operate on an external power source, their range of transportability is quite limited. Further, it happens that electrical pumps are generally more complicated to use and more difficult to maintain than are purely mechanical pumps.
Of the numerous mechanical structures which have been proposed for use as a pumping chamber in portable IV infusion pumps, one structure is of particular interest. This structure is an elastomeric membrane. Indeed, an elastomeric pumping mechanism has several features which make it attractive for such an application. Firstly, an elastomeric structure is relatively inexpensive to manufacture. Secondly, it has an operational simplicity which enhances its appeal for use in devices which are to be operated by lay persons. It happens, however, that despite the simplicity of such a device not much is known or appreciated about how an elastomeric membrane works or how it can be employed with maximum efficiency.
Several examples of elastomeric pumping mechanisms for portable pumps can be cited in which various configurations for the elastomeric material are suggested. In some instances, such as for the devices disclosed in U.S. Pat. No. 4,769,008 to Hessel, and U.S. Pat. No. 4,419,096 to Leeper et al., the elastomeric membrane is tubular shaped. In other instances, such as for the device disclosed in U.S. Pat. No. 5,019,047 to Kriesel the membrane is formed as a sheet. In each case, the membrane either creates or is established as part of the fluid chamber. Consequently, subsequent to filling the chamber with fluid to stretch the membrane, the membrane is allowed to contract and thereby create fluid pressure within the chamber to pump the fluid from the chamber. Furthermore, it has been suggested that the extent of collapse of an elastomeric pumping chamber be limited. Ostensibly this is done to maintain a pressure on the fluid in the chamber at the end of the operational cycle which will cause most of the fluid to be pumped or dispensed from the chamber. This, however, does not address the problem encountered at the end of a pumping cycle which is caused by the inability of an elastomeric membrane to maintain a constant pressure within the fluid chamber as the membrane approaches its unstretched state. As is well known, constant pressure within the pumping chamber during a pumping operation is very much desired to obtain a uniform dispensing rate.
In order to maintain constant pressure on fluid during an infusion operation with a contracting elastomeric membrane, it is necessary to properly design the environment within which the elastomeric membrane will operate. This, or course, must take into account the physical capabilities of the membrane. Presently, there are no known portable infusion pumps which structurally establish the operational parameters for the collapsed state of an elastomeric pumping chamber. Consequently, portable infusion pumps that rely on the influence of a contracting elastomeric membrane to infuse fluids to a patient do not maintain the elastomeric pumping mechanism in its optimal operational mode throughout the pumping cycle. The present invention recognizes that these considerations are extremely important.
In light of the above, it is an object of the present invention to provide a portable IV infusion device which is easily transported by its user. Another object of the present invention is to provide a portable IV infusion device which is reliable and which establishes an acceptably accurate fluid infusion rate having a substantially constant flow profile. Still another object of the present invention is to provide a portable IV infusion device which provides a substantially constant pumping pressure throughout a predetermined duration for the operation of the device. Another object of the present invention is to provide an IV infusion pump which infuses fluids with substantially no residual volume in the chamber of the pump after the pumping operation has been completed. Yet another object of the present invention is to provide a portable IV infusion device which can be prefilled and stored in a ready-to-use configuration for a relatively extended period of time while maintaining sterility of the fluid medicament that is held in the chamber of the device. Still another object of the present invention is to provide a disposable infusion device having a pumping chamber which can be filled to different volumes and still maintain the same fluid delivery rate regardless of the initial fill volume. Another object of the present invention is to provide a portable IV infusion pump which is easy to use, relatively simple to manufacture and comparatively cost effective.